Thyroid-stimulating hormone is associated with insulin resistance independently of body mass index and age in women with polycystic ovary syndrome

BACKGROUND: The aim of this study was to evaluate the association between thyroid function, reflected by thyroid-stimulating hormone (TSH) levels, and insulin resistance (IR) in 337 women suffering from polycystic ovary syndrome (PCOS). METHODS: Clinical, metabolic and endocrine parameters were obtained and an oral glucose tolerance test was performed, with calculation of IR indices. The association between thyroid function and IR was evaluated with classification analysis using logistic regression and 10-fold cross-validation to identify a possible TSH threshold for IR. Parameters were then compared between women above and below the TSH threshold using two-sample tests. One-way analyses of covariance were performed to explore whether the impact of TSH on IR is independent of other variables. RESULTS: A TSH cut-off value around 2 mIU/l had the best sensitivity and specificity for identifying women with IR. Women with TSH >= 2 mIU/l were younger, had a higher body mass index (BMI) and were more insulin-resistant compared with women with TSH < 2 mIU/l. This effect of TSH on IR was independent of age and BMI. CONCLUSIONS: In women with PCOS, a significant association between thyroid function, as reflected by TSH >= 2 mIU/l, and IR was found and the association appeared to be independent of age and BMI.